Mitt Romney's tax returns reveal that the Republican presidential candidate does something fewer Americans do these days: He tithes.

Romney's 2009 and 2010 tax returns, released Tuesday, show that he and his wife, Ann, gave 10 percent of their income, about $4.1 million, to the Church of Jesus Christ of Latter-day Saints. The couple reported income of about $43 million for the two years.

LDS church members must tithe to participate in temple rituals. Nearly 80 percent of Mormons tithe, a poll released this month by the Pew Forum on Religion and Public Life shows.

While tithing among Mormons is high, it is at an all-time low – less than 3 percent – among many faith groups, according to an October report by Empty Tomb, a Christian research organization. The theology behind tithing is also being questioned, with many saying the mandate to contribute 10 percent is not biblical.

Tithing has its roots in the Old Testament – "Bring all the tithes to the storehouse," from the book of Malachi – and means one-tenth of income.

"The New Testament says a Christian is saved under grace and it does not teach tithing," said Russell Kelly who argues against it on his website, www.shouldthechurchteachtithing. com. "A lot of people would rather stay home than go to church and hear about it. All it does is make them feel as if they're cursed for not giving 10 percent."

About 58 percent of evangelical leaders do not believe the Christian Bible requires tithing, according to a study last April conducted by the National Association of Evangelicals. They do however, believe Christians should give generously.

Kelly and others promote "sacrificial giving" – giving in proportion to what God has given them. "Ten percent may not mean anything to someone who is really rich, but it will mean a lot to a person without a job," Kelly said. "The person who has more, should give more."

The Rev. Rick Gregory, pastor of Grace Bible Church of Fair Oaks, said tithing as mentioned in the Old Testament is not law. "Christians should give out of gratitude," he said. "Not out of meeting a legal obligation."

He said Christians should give as an expression that "all we have belongs to the Lord."

Christians, on average, give 2.38 percent of their income to churches, a figure that has dropped steadily in recent years, said Sylvia Ronsvalle, executive vice president of Empty Tomb, which has tracked tithing and giving to religious organizations since 1968.

She said the recession is only partly to blame for the decline. "There does not seem to be a pattern between previous economic recessions and giving," Ronsvalle said.

She said churches are also keeping more of their donations for their own needs, and so-called "benevolence spending," such as overseas missions, has dropped.

Ronsvalle is concerned about the overall effect the decline in giving will have. She said most people make their charitable donations to religious organizations.

"If giving to religion is declining, then it's going to have an impact on the total charitable sector in the United States."

Tithing and collecting money is a sensitive issue in many churches. Many churches no longer pass collection plates during worship services. Instead they have boxes or baskets sitting at the back of the church. At the end of the service, they ask believers to give what they can.

"If more churches did this, I think they'd find that more people would come in and so would their money," Kelly said.

Tithing among Mormons remains high because members view it as essential to their faith, said Richard Montgomery, public affairs director for the LDS church in the region. In the Sacramento area, about 20,000 members give 10 percent to the church, he said.

Members pay their tithes to the bishop and that money is forwarded to church headquarters in Salt Lake City. These donations are used to fund construction of temples and building maintenance, and to support social service organizations such as the 300 employment centers overseen by the church.

Members are also expected to donate "fast offerings." Once a month, they skip two meals in a 24-hour period and that money is given to their bishop. He uses that money to help local church members.

Romney's family has been prominent in the church for generations. Over the past decade, Romney and his wife have given more than $4.7 million to the church through the Tyler Charitable Foundation, a trust the couple oversees.

The former Massachusetts governor talked about tithing last weekend on "Fox News Sunday."

"The Bible speaks about providing tithes and offerings. I made a commitment to my church a long, long time ago that I would give 10 percent of my income to the church. And I followed through on that commitment," Romney said. "And, hopefully, as people look at various individuals running for president, they'd be pleased with someone who made a promise to God and kept that promise."